1. Field of Art
The present invention relates to a high quality polyetherimide/epoxyimide resin composition having a utility for various applications due to its improved resistance to heat, high adhesiveness at elevated temperature and low moisture permeability.
2. Statement of the Prior Art
Polyimides are generally excellent in thermal resistance (resistance to heat), and thus have been used as materials for space and aircraft applications. However, most of the known polyimides are prepared through polycondensation reactions, and water or other side-reaction products are produced during the polycondensation reactions. The other disadvantage of these known polyimide resins is that they are often insoluble in any solvent and also infusible, leading to poor moldability. In other words, difficulties are encountered in molding the known polyimide resins. On the other hand, epoxy resins are thermosetting resins or may be hardened by the use of hardeners, and may be easily molded. However, thermal resistivities of the known epoxy resins are not yet satisfactory.
It has been eagerly pursued to develop a resin composition which have the advantageous thermal resisting property of the polyimide resins together with the advantageous moldability of the thermosetting epoxy resins. One approach for achieving such an object is to introduce a chemical structure or chemical moiety which is expected to attribute for the improvement in molding property of the resultant resin into a certain polyimide, and another approach is to improve the thermal resistivity of an epoxy resin having excellent molding property.
Also known in the art is the utilization of polyimides as adhesives, while making use of their excellent thermal stabilities or resistivities. For example, SAMPE (Society for the Advancement of Material and Process Engineering), Quarterly Volume 13, pages 20 to 25 (October, 1981), discloses an adhesive of polyimide system, which has a tensile shearing adhesive strength of not less than 100 kgf/cm.sup.2 even at a high temperature. However, since the adhesive disclosed by the aforementioned prior art reference requires that it must be used at a temperature of not lower than 300.degree. C. for its use as an adhesive, the materials to be bonded thereby should withstand a temperature of not lower than 300.degree. C. It is thus demanded to develop an adhesive which may be used as an adhesive having excellent thermal resistivities and yet can be applied at a moderately lower temperature for the exhibition of its adhesive property.
A further disadvantage of the polyimides is that they are relatively higher in moisture permeability when compared to those of the epoxy resins. Accordingly, when a polyamide is used to form an insulating layer in an electrical device or instrument, the coating layer tends to absorb moisture in the atmosphere to be lowered in its insulation resistance to cause occationally a problem of inferior connection or to induce corrosion of the electrodes. There is thus a demand for the development of a polyimide resin composition having low moisture permeability.